It has recently been reported that inorganic compound materials having size, thickness, shape, etc. controlled at nanometer scales (hereinafter referred to as nano scales) can remarkably improve chemical, mechanical, and optical properties of surfaces. Then nanotechnology has actively been studied in the fields of fluorescent materials, magnetic materials, production of various sensors, high-density electronic devices, etc. To create such nano materials, bottom-up synthesis processes from atoms and molecules are needed. Particularly, technologies for designing composition and structure of metal nanoparticles and ultrathin films at a molecular or atomic level can be important, fundamental technologies in various fields.
Known methods for synthesizing the metal nanoparticles controlled at nano scales include methods of reducing metal ions under the presence of stabilizers in uniform solutions, and methods of reducing metal ions in matrixes of uniform polymers.
For example, a method of temporarily using a stabilizer and a reducing agent to produce a metal microparticle has been known (JP-A-2002-146235, claim 11 and Paragraphs [0013] to [0028]). This method can produce a noble metal-containing microparticle having a low impurity content sufficiently for use in fuel cells. However, this method comprises the complicated steps of adding the stabilizer and the reducing agent and removing the added stabilizer and reducing agent, whereby the method cannot be a simple method of producing the metal nanoparticles.
Further, a method of producing a metal nanoparticle in a polymer having a polar group has been known (JP-A-9-188778, claims 1 to 13 and Paragraphs [0007] to [0028]). However, in this method, a metal ion has to undergo ion exchange in the polymer, whereby the polymer must have an ion-exchangeable polar group. Thus, the polymer used in this method is limited, and polymers with no ion-exchangeable polar groups cannot be used.
The inventors have developed a method for easily synthesizing a metal nanoparticle using a metal oxide in a support (He, Kunitake, et al., “In Situ Synthesis of Nobel Metal Nanoparticles in Ultrathin TiO2-Gel Films by a Combination of Ion-Exchange and Reduction Processes”, Langmuir, 2002, 18, pp 10005-10010). However, the support used in this method is not an organic component support but a TiO2 thin film. Further, a metal ion has to be exchanged also in this method like JP-A-9-188778, so that the method has a disadvantage of restriction in the matrix.
As described above, a satisfactory method capable of certainly forming a metal nanoparticle from an easily-available, natural or synthetic, organic material with ease and excellent accuracy has not been developed. Under such circumstances, an object of the present invention is to provide a supported metal nanoparticle and a method for producing the same, wherein a metal nanoparticle can be easily obtained in situ with excellent accuracy using a various natural or synthetic organic material as a matrix. Another object of the invention is to provide a continuous metal nanoparticle body easily produced using a natural or synthetic organic material and a method for producing the same.